The Missouri Lead (irid Zinc Deposits. — Iioh('vls(jn. 241 
of the mines, the galena is concentrated to a greater or less 
extent in certain strata, while in other deposits there appears 
to be no regularity in the concentration of the ore. As a rule 
there are no well defined limits to the ore body, but the min- 
eral contents of the rock graduall}' decrease until it is un- 
profitable to work. Only traces of zinc have been found in 
these mines, but iron and copper pyrites are found in limited 
quantities and these contain small amounts of nickel and co- 
balt, which have hitherto been saved. Manj' small crevices 
are noticed in these mines, but they die out in depth and 
could consequently have played no part as carriers of ascend- 
ing solutions. Some faulting was noticed in one of the mines 
of this district. Though the ore deposits are frequently in 
proximity to such lines of disturbance, but little ore is found 
on the plane of the main fault and the others were of small 
throw and apparently of slight significance. 
The crevice deposits of this and of the central district are 
totall}'- different in appearance from these massive deposits. 
They are often horizontal and consist of a network of small 
channels opening into larger or chimnej^-shaped bodies. The 
ore occurs usually in a gangue of cla}' or barite. Some of 
these deposits are of the vertical or vein type and show un- 
mistakable evidences of faulting. These are quite narrow and 
are filled with barite and clay in which the galena occurs. 
The Virginia mine in Franklin county was followed to a depth 
of 480 feet, but the crevice was only 4 to 6 inches in width. 
There is one other variety of deposits, found in the central 
district and kiu^wn as the circle type. In this the ore body is 
of a rudely conical shape, barren limestone being found on the 
exterior walls, and, in the interior, a circular mass of barren or 
nearl}'^ barren limestone debris. The galena is found in the 
breccia filling the circular space, attached to the limestone and 
associated with barite and caleite. 
In attempting to account for the origin of these deposits 
the first question to be disi)osed of is that of the fornuUion of 
the cavities in which the minerals are found. 'I'hese cavities 
are of two kinds: 1) vertical or transverse to the strata; 2) 
horizontal or between the strata. 
The various movements of the earth have, as already inti- 
mated, given rise to flexures and faults, generall}' small in 
